Remote vehicle emissions sensing system and method for differentiating water from hydrocarbons

ABSTRACT

Water droplets in exhaust gas that is, or was, analyzed by a remote emissions sensing system are detected. The detection may be made using measurements generally captured by the remote emissions sensing system during typical operation. As such, the detection may be applied “on site” as remote emissions sensing analysis is ongoing, or may be applied post hoc from data previously acquired by a remote emissions sensing system. The detection may be implemented without requiring additional sensors, more sophisticated sensors, and/or other additional or more sophisticated equipment being included in the remote emissions sensing system.

FIELD OF THE INVENTION

The invention relates generally to the remote measurement of vehicleemissions, and more particularly to a system and method for thedetection of water droplets in remotely monitored vehicle emissions.

BACKGROUND OF THE INVENTION

Systems and methods for remotely monitoring the exhaust gas compositionof motor vehicles are known. For example, a Remote Sensing System (RSS)positioned at a predetermined location along a roadway measures tailpipeemissions as vehicles pass through infrared (IR) and ultraviolet (UV)beams cast across the roadway. IR/UV light is typically reflected backacross the roadway (e.g., via a transfer mirror module) to a series ofdetectors that monitor light intensity at characteristic wavelengths. Bymeasuring the absorption of IR/UV light by the various pollutants in theair, the RSS is able to calculate pollutant concentrations in theexhaust plumes of passing vehicles.

More particularly, RSS exhaust emissions measurements comprise a seriesof periodic readings spanning a predetermined time period (e.g.,approximately one-half second after the passing of a vehicle). Eachreading gives the quantity of each gas of interest (e.g., in an exhaustplume) in the beam path. Because the amount of dilution of an exhaustplume at each instant is not known, the individual readings for each gasare ratioed, for example, to a corresponding carbon dioxide (CO₂)reading. These ratios of gas amounts remain constant throughout anexhaust plume, and are independent of dilution. The ratios themselvesmay be useful. For example, the ratios may be directly converted to massof pollutant per mass of fuel, or can be used in conjunction with thecombustion equation to convert the ratios into the gas concentrationswhich would be measured by a tailpipe probe when corrected for excessair and water. A combustion equation that assumes a particular fuel isused to convert the ratios into gas concentrations.

Remote emissions measurements rely on the ability of each gas ofinterest to absorb light of only certain wavelengths. A channel (foreach gas of interest) compares the amount of light traversing the beampath in its particular frequency before the vehicle with the amount oflight after the vehicle, and calculates the amount of gas from theabsorbed light. To correct for fluctuations in the light source or lightthat may be blocked by particles, a reference channel is also used at afrequency where there is no gaseous absorption.

Over time, steady advances in the sophistication and robustness ofremote sensing technology, together with the analysis of acquiredvehicle emissions data, have resulted in a number of important findings.As an example, it has been determined that the presence of waterdroplets in vehicle exhaust emission plumes may cause erroneously highhydrocarbon (HC) readings. This may be especially problematic whenattempting to measure evaporative emissions (e.g., vapors that vent intothe air from hot engines and fuel systems) by noting high HC readingsthat are uncorrelated with accompanying CO₂ readings.

One prior approach for recognizing and rejecting erroneously high HCreadings in remote emissions measurements includes the use of anadditional IR channel that is twice as sensitive to water droplets as itis to gaseous HC. See WILLIAMS, Mitchell Jared, “Advances in On-RoadRemote Sensing: Feat 5000 The Wert Generation”, Thesis, University ofDenver, MAS 2003 No. 27, August 2003, which is hereby incorporatedherein by reference in its entirety. Detections of elevated HC in the HCchannel accompanied by readings that are twice as elevated in theadditional IR channel are flagged as water droplet “steam” plumes. Useof this hardware-based approach, however, may result in both anincreased time and expense associated with hardware configuration and/orcalibration.

These and other drawbacks exist.

SUMMARY OF THE INVENTION

The invention addressing these and other drawbacks relates to a systemand method for the detection of water droplets in remotely monitoredvehicle emissions, including both exhaust emissions and evaporativeemissions. The detection may be made using emissions data acquired by anRSS during typical operation. Accordingly, the detection may be made inreal-time as data is acquired, or during post-processing of apreviously-acquired emissions data set. Further, the system and methodof the invention enable the detection of water droplets in remotelymonitored vehicle emissions data without modifying an RSS to includeadditional sensors (or components) and/or more sophisticated sensors (orcomponents).

According to an aspect of the invention, and as described in greaterdetail herein, an RSS system may comprise an electromagnetic radiationsource, a detector, one or more processors, and/or other components. Thesource and detector may be configured such that an optical path betweenthe source and the detector traverses a roadway along which a vehicleemitting exhaust gas travels. The source may emit electromagneticradiation at wavelengths that are absorbed by a plurality of molecularspecies present in vehicle exhaust emitted by the vehicle. The molecularspecies may include, for example, hydrocarbons (HC), carbon monoxide(CO), carbon dioxide (CO₂), nitrogen oxides (NO_(X)) such as NO and NO₂,and/or other molecular species.

As such, the wavelengths at which electromagnetic radiation is emittedby the source and absorbed by molecular species may include a firstabsorption wavelength, a second wavelength, a third absorptionwavelength, and/or additional absorption wavelengths. The firstabsorption wavelength may be a wavelength at which CO absorbselectromagnetic radiation, the second absorption wavelength may be awavelength at which CO₂ absorbs electromagnetic radiation, and the thirdabsorption wavelength may be a wavelength at which HC absorbselectromagnetic radiation.

For instance, CO may absorb electromagnetic radiation at or near 4.6microns (e.g., the first absorption wavelength), HC may absorbelectromagnetic radiation at or near 3.6 microns (e.g., the secondabsorption wavelength), and CO₂ may absorb electromagnetic radiation ator near 4.3 microns (e.g., the third absorption wavelength). These areprovided merely for illustrative purposes. In some implementations,other particular molecular species may be used in accordance with thisdisclosure for the purposes of detecting the presence of water.

The electromagnetic radiation emitted by the source may further includeelectromagnetic radiation at one or more reference wavelengths. The oneor more reference wavelengths may include wavelength(s) at whichelectromagnetic radiation is not substantially absorbed by any of theconstituents commonly found in vehicle exhaust. For example, thereference wavelength may be at or near 3.9 microns.

According to an aspect of the invention, the one or more processors maybe configured to provide information processing capabilities in thesystem. The one or more processors may be provided along with the sourceand the detector for analysis at a testing site. In someimplementations, the one or more processors may include a first set ofone or more processors physically present at the testing site, and asecond set of one or more processors that process data acquired and/orprocessed at the testing site remotely in time and/or space from theacquisition of data at the testing site. Information may be transferredbetween the first set of processors to the second set of processors by acommunication link, via removable electronic storage, and/or by othercommunication mechanisms.

The one or more processors may be configured to execute one or morecomputer program modules. The one or more computer program modules mayinclude one or more of a quantity module, a ratio module, a triggermodule, a residual module, a water analysis module, and/or othermodules. The one or more processors may be configured to execute themodules by software, hardware, firmware, some combination of software,hardware, and/or firmware, and/or other mechanisms for configuringprocessing capabilities on the one or more processors.

In one implementation, the quantity module may be configured todetermine preliminary quantities of one or more molecular species in theoptical path. The quantity module may make this determination based onoutput signals generated by the detector indicating the intensity ofelectromagnetic radiation received at the detector in one or moreabsorption wavelengths. The intensities of the electromagnetic radiationreceived in the one or more absorption wavelengths may indicate amountof electromagnetic radiation in the one or more absorption wavelengthsthat have been absorbed and/or blocked along the optical path.

During operation, the intensities of electromagnetic radiation emittedby the source may vary. Such variation may be the result of ordinaryoperation, and/or may be enhanced by environmental and/or systemfactors. To account for these variations, the detector may generate oneor more output signals indicating the received intensity of one or morereference wavelengths. Since electromagnetic radiation at the one ormore reference wavelengths may not be significantly absorbed by exhaustgas, the quantity module may implement these output signals of thedetector to correct for variation in the intensity of electromagneticradiation emitted by the source.

In one implementation, the ratio module may be configured to determineratios of the molecular species for which quantities are determined bythe quantity module. The dilution of exhaust gas present in the opticalpath may not be known at a given point in time. As such, to determinethe concentrations of molecular species, the ratio module determinesratios of molecular species because such ratios may be independent ofdilution. For example, the ratio module may determine a ratio of CO toCO₂, and/or a ratio of HC to CO₂. The ratios determined by the ratiomodule may be converted to concentrations of the molecular species froma combustion equation that assumes a particular fuel.

Generally, vehicle exhaust includes relatively large quantities ofwater. When the water is in a gaseous state, the water may notsubstantially interfere with measurements of exhaust gas composition bythe RSS. However, under certain ambient conditions, such as lowtemperatures and/or high humidity, for example, gaseous water present inexhaust may undergo a phase change and form minute liquid dropletshaving the appearance of white smoke, sometimes incorrectly referred toas “steam” or a “steam plume”. These droplets may effectively blockelectromagnetic radiation at various wavelengths from ultra-violetspectrum, through the visible spectrum, and into the near infra-redspectrum. The wavelengths at which the liquid water blockselectromagnetic radiation may include wavelengths at whichelectromagnetic radiation is absorbed by one or more gaseous species inexhaust gas.

For example, in the spectrum from about 3 microns to about 5 microns,water droplets present in the optical path may block electromagneticradiation. This portion of the spectrum may include the first absorptionwavelength (e.g., corresponding to CO), the second absorption wavelength(e.g., corresponding to HC), a third absorption wavelength (e.g.,corresponding to CO₂), and/or a reference wavelength as described above.In this portion of the spectrum, the ability of water droplets to blockelectromagnetic radiation may fall as wavelength increases. This drop inblockage of electromagnetic radiation by water droplets may besubstantial for increasing wavelengths. As such, water droplets in theoptical path may tend to have a very different impact on theelectromagnetic radiation in the optical path at the first absorptionwavelength, the second absorption wavelength, the third absorptionwavelength, and/or the reference wavelength. This may negatively impactthe accuracy of the quantity module and/or the ratio module.

In one implementation, the trigger module may be configured to triggeranalysis to determine if water droplets are present in the optical pathat a given point in time. This may include analyzing determinations ofabsorption and/or quantity of one or more molecular species forapparently anomalous readings. By way of non-limiting example, theamount of blockage caused by water droplets in the optical path may bemuch larger at the second absorption wavelength than in the referencewavelength. As was discussed above, the quantity module may implementthe reference wavelength in correcting absorption at the secondabsorption wavelength to account for intensity variations at the source.This may result in determinations of apparent absorption at the secondabsorption wavelength (and/or of quantity of HC) that are higher thanthe actual amount of absorption (and/or quantity of HC).

In some implementations, the trigger module may monitor determinationsof absorption at the second absorption wavelength and/or determinationsof quantity of HC. The trigger module may trigger analysis to determineif water is present in the optical path if absorption at the secondabsorption wavelength and/or the quantity of HC are elevated. Forexample, further analysis may be triggered by the trigger module ifabsorption at the second absorption wavelength and/or the quantity of HCbreach a predetermined threshold.

Because of the fall off in blockage by water droplets at ascendingwavelengths, the blockage by water droplets will tend to impactdeterminations of absorption for absorption wavelengths other than thesecond absorption wavelength differently than determinations ofabsorption for the second absorption wavelength. This may enable theresidual module and the water analysis module to detect the presence ofwater droplets in the optical path from a comparative analysis based onthe determined absorptions at the various absorption wavelengths.

The impact of water droplets on the determination of absorption forabsorption wavelengths that are larger than the second wavelength may berelatively small with respect to absorption by exhaust gas along theoptical path at the larger absorption wavelengths. As such, before theimpact of water droplets on the determinations of absorption forabsorption wavelengths other than the second absorption wavelength canbe used to detect the presence of the water droplets, the impact of thewater droplets must be separated from the absorption by the exhaust gas.

In one implementation, the residual module may be configured to separatethe actual absorption by exhaust gas from residual impact onelectromagnetic radiation intensity caused by water droplet blockage atone or more absorption wavelengths. For example, to quantify theresidual impact of water droplet blockage at the first absorptionwavelength, the quantity of CO may be determined as a function of themeasured quantity of another molecular species, such as CO₂. Thisdetermination may be made, for instance, by a regression line thatcorrelates values of the quantity of CO determined by the quantitymodule with values of the quantity of CO₂ determined by the quantitymodule from contemporaneous measurements.

Once the quantity of CO as a function of CO₂ is determined, the residualimpact which may be caused by water droplet blockage at the firstabsorption wavelength (separate from absorption by the first molecularspecies) may be determined according to the following relationship:CO_(residual)=CO_(measured)−(α+m*CO_(2measured))  (1)

where CO_(residual) represents the residual impact of water dropletblockage at the first absorption wavelength on the determination of thequantity of CO;

CO_(measured) represents the quantity of CO determined by the quantitymodule;

CO_(2 measured) represents the quantity of CO₂ determined by thequantity module; and

(α+m*CO_(2measured)) represents an equation by which the quantity of COcan be determined as a function of CO_(2measured).

Water droplets formed from exhaust gas will typically only be present inthe optical path for a short period of time. As such, the correlation ofCO_(measured) with CO_(2measured) to determine CO(CO_(2measured)), whichuses measurements of CO_(measured) and CO_(2measured) over a far greaterperiod of time than will be impacted by the water droplets, may alsotend to reflect the relationship between CO_(measured) andCO_(2measured) when water droplets are not present in the optical path.For the purpose of calculation of CO_(residual), if a negativecorrelation slope is obtained (m<0), then the negative in may bereplaced with 0 in equation (1).

In one implementation, the water analysis module may be configured toanalyze the residual impact of water droplet blockage at the firstabsorption wavelength on the determination of the quantity of CO and thequantity of HC made by the quantity module to determine if water dropletblockage is/was present in the optical path. For instance, the residualimpact of water droplet blockage at the first absorption wavelength onthe determination of the quantity of CO may be compared with thequantity of HC to determine if the values of both of these variablesindicate the presence of water droplet blockage in the optical path.

By way of non-limiting example, the impact of water droplet blockage ondeterminations of HC may be inversely proportional to the impact ofwater droplet blockage on determinations of CO_(residual). In the caseof HC and CO, the proportionality factor may be on the order of −10⁻⁴.

It will appreciated that the description of various implementationsherein with respect to the specific molecular species CO, HC, and CO₂are not intended to be limiting. Other implementations in whichdifferent molecular species are associated with a different firstabsorption wavelength, second absorption wavelength, and/or thirdabsorption wavelength fall within the scope of this disclosure.

These and other objects, features, and characteristics of the invention,as well as the methods of operation and functions of the relatedelements of structure and the combination of parts and economies ofmanufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only, andare not intended as a definition of the limits of the invention. As usedin the specification and in the claims, the singular form of “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary illustration of an RSS system, according to anaspect of the invention.

FIG. 2 is an exemplary illustration of an RSS system, according to anaspect of the invention.

FIG. 3 illustrates an example of a plot of absorption (in an absorptionwavelength) versus time, according to an aspect of the invention.

FIG. 4 is an illustrative depiction of a regression line that correlatesdetermined quantities of a first molecular species with determinedquantities of another molecular species, according to an aspect of theinvention. The CO_(residual) of each point is the distance up or down ofeach CO point from the line. In the illustration shown in FIG. 4,a˜0.145, and m˜0.0312.

FIG. 5 illustrates plots of the residual impact of water dropletblockage at a first absorption wavelength on the determination of thequantity of a first molecular species and of the determined quantity ofanother molecular species versus time, according to an aspect of theinvention. A strong anticorrelation between HC and CO_(residual) can beseen, and may illustrate that he observed apparently large HC is causedby water droplets (e.g., a steam plume).

FIG. 6 is an exemplary illustration of a flowchart of processingoperations for detecting the presence of water droplets in the opticalpath of an RSS system, according to an aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Prior to describing an exemplary method for the detection of waterdroplets in remotely monitored vehicle emissions, including both exhaustemissions and evaporative emissions, a description of an exemplary RSSwill first be provided. Various implementations of the invention mayinclude some or all of the RSS components as described below.

Exemplary Remote Sensing System (RSS)

FIG. 1 illustrates RSS 110 according to an implementation of theinvention. RSS 110 measures emissions in an exhaust plume 112 (from amotor vehicle 114) in an optical (or measurement) path 130 on a roadway128. Roadway 128 may comprise a single or multi-lane roadway, or anyother roadway or driving surface suitable for the safe passage ofvehicle 114 under various operating conditions. Alternatively, roadway128 may comprise a test lane designated for vehicle emissions testing,wherein vehicle 114 may be tested under a variety of operatingconditions. RSS 110 may comprise a source 116, a detector 118, aprocessor 122, and/or other components.

As previously recited, source 116 may comprise one or more sources ofelectromagnetic radiation (ER) and detector 118 is preferably chosen topermit detection of electromagnetic radiation emitted by source 116.Source 116 may be selected to provide electromagnetic radiation withspectral characteristics that facilitate the detection of one or morepredetermined gases present in exhaust plume 112. For example, nitricoxide, ammonia, and sulfur dioxide may be measured using UVelectromagnetic radiation. Nitrogen dioxide, for example, may bemeasured using electromagnetic radiation with a wavelength of 430 nm.

According to one implementation, RSS 110 may comprise transfer optics120 configured to allow radiation from source 116 to be directed todetector 118 for analysis. Transfer optics 120 may comprise a mirror,flat mirror, lateral transfer mirror (LTM), vertical transfer mirror(VIM), retroflector, or other device. In one implementation, transferoptics 120 may comprise a lateral transfer mirror to reflect radiationfrom source 116 along a path displaced laterally or vertically,depending on orientation, from the incident direction. Otherconfigurations may be used.

Processor 122, as will be described further below, may employ softwareto accomplish desired analysis of collected and/or stored data, and tocarry-out one or more of the processing operations described herein.Processor 122 may include one or more of a digital processor, an analogprocessor, a digital circuit designed to process information, an analogcircuit designed to process information, a state machine, and/or othermechanisms for electronically processing information. Although processor122 is shown in FIG. 1 as a single entity, this is for illustrativepurposes only. In some implementations, processor 122 may include aplurality of processing units. These processing units may be physicallylocated within the same device, or processor 122 may representprocessing functionality of a plurality of devices operating incoordination. For example, in some implementations, processor 122 mayinclude a first set of one or more processors physically present at aremote testing site at which source 116 and detector 118 are deployed,and a second set of one or more processors that process data acquiredand/or processed at the testing site remotely in time and/or space fromthe acquisition of data at the testing site. Information may betransferred between the first set of processors to the second set ofprocessors by a communication link, via removable electronic storage,and/or by other communication mechanisms.

With regard to an exhaust gas sample present in optical path 130,software may be used to calculate the relative amounts of variousexhaust gas constituents, concentrations of various exhaust gasconstituents (e.g., HC, CO₂, NO_(x), CO, etc.), the decay rate (e.g.,dissipation in time) of the exhaust constituents, and the opacity of theexhaust plume.

Processor 122 may further comprise software to accomplish other dataanalysis functions. For example, vehicle emission data may be checkedfor running losses. Running losses may typically include emissionreadings due to fuel system leaks on a vehicle (e.g., leaky fuel tankfiller cap, fuel line, etc.), blow-by emissions (e.g., crank caseemissions blowing by the piston rings), or other systematic losses.

Processor 122 may also include software to accomplish various vehicleowner notification functions. For example, the owner of a vehicle thathas been recorded as being in compliance with certain predeterminedemission levels may receive a notification (e.g., via regular mail,electronic mail, text message, facsimile, recorded telephonecommunication, or the like). Coordination with local authorities may bearranged to grant vehicle owners a waiver or pass of local emissioncertification procedures upon receiving such a notification. Likewise,vehicles that fail to meet predetermined emission levels may receive anotification requiring the owner to remedy the non-compliance. Otherdata processing functions are also possible. Processor 122 may alsointerface to, control, and/or collect and reduce data from an imagingunit 132, a speed and acceleration detection unit 134, and thermaldetection unit 136.

In various implementations, RSS 110 may comprise an imaging unit 132 tocapture and/or record an image of vehicle 114 passing by (or through)RSS 110 in a known manner. Imaging unit 132 may be positioned to recordan image of vehicle 114 at any predetermined number of locations.Imaging unit 132 may comprise, for example, a film camera, video camera,or digital camera. Other imaging devices may also be used.

In one implementation, imaging unit 132 may record an image of theidentification tag (e.g., license plate) of vehicle 114. Tag informationmay be processed by processor 122 to provide additional informationabout the vehicle. For example, Motor Vehicle Department databases maybe accessed to retrieve owner information, make, model type, model year,or other information. In some implementations, this additionalinformation may be incorporated into the emission sensing data analysis.For example, the make and model year of the vehicle may be used todetermine input information for certain processing steps, includinginformation such as whether the vehicle includes a carburetor or fuelinjector, whether the car runs on diesel fuel or gasoline, etc.

According to an implementation of the invention, RSS 110 may include aspeed and acceleration detection unit 134, Preferably, the speed and/oracceleration of vehicle 114 may be measured as it passes through RSS 110using speed and acceleration detection unit 134 in a known manner.

In one implementation, speed and acceleration detection unit 134 maycomprise an arrangement of laser beams or other light beams associatedwith timing circuitry. The laser or light beams may be arranged totraverse the path of vehicle 114 at various points. As vehicle 114passes, it will cause interruptions in the laser or light beams. Thetimes at which the beam interrupts occur may be used to calculate thevehicle's speed and/or acceleration. Other methods of determiningvehicle speed and/or acceleration may also be used or incorporated intoRSS 110.

Alternatively, the laser or light beams or radar beams may be arrangedto intercept the path of vehicle 114 as it drives along roadway 128. Forexample, radar systems may be used to determine vehicle speed andacceleration. Alternatively, transducers, piezoelectric elements, orother “drive over” detectors may be placed at locations in the roadwayto monitor vehicle passage. Preferably, speed and/or acceleration datamay be input into processor 122 to help characterize vehicle operatingconditions (e.g., accelerating or decelerating), or to determine whichvehicle is to be associated with a particular sensor measurement. Otherconfigurations and uses of speed and acceleration data are alsopossible.

Some implementations of the invention may incorporate a thermaldetection unit 136. Preferably, thermal detection unit 136 may comprisea non-contact thermometer system. For example, an IR thermometer may beused to optically detect the temperature of remote objects. Othertemperature detection systems may also be used. Thermal detection unit136 may, for example, be used to detect the temperature of portions ofthe vehicle passing through RSS 110. Some implementations may use directsensing of the area of interest. For example, an IR thermometer may beaimed at the underside of a passing vehicle to detect the temperature(s)of vehicle components (e.g., engine, catalytic converter, muffler,etc.). Indirect sensing may also be used. For example, an IR thermometermay be aimed at the roadway to measure the heat of the passing vehiclewhich is reflected from the roadway surface.

Thermal information that is detected by thermal detection unit 136 maybe used to indicate that an engine has just recently been started (e.g.,the engine is “cold” or has not reached normal operating temperature).Such a cold engine reading may be used, for example, to initiate analternative data processing routine. Certain implementations of theinvention may reduce the chance of a potentially misleading reading byalso detecting the temperature of other portions of the vehicle. Otheruses for collected thermal data are also possible. Thermal detection ofthe exhaust plume of a vehicle and/or ambient temperatures may also beused in connection with various aspects of the invention.

According to one implementation of the invention, an identification tagon vehicle 114 may be read to identify the vehicle and associateparticular sensed vehicle emission information with the vehicle. Anidentification tag, defined as a license plate above, may also comprisea transponder located on or within vehicle 114 (e.g., hung from a rearview mirror, placed on the dashboard, etc.), or that is integral withinthe vehicle (e.g., part of a global positioning system (“GPS”), locatedwithin the engine of the vehicle, or placed or mounted elsewhere). Thetransponder may transmit information about vehicle 114, including makeand model of vehicle 114, engine characteristics, fuel type, the ownerof vehicle 114, or other information which may be pertinent. Accordingto an implementation, a transponder may be used in connection with otherfunctions. For instance, a transponder may also be used in connectionwith a toll pass, whereby a driver can electronically pay tolls via thetransponder without stopping the vehicle.

An identification tag may also comprise a tag or decal that requires areader. By way of example, an identification tag may comprise a decalwith identifying marks (e.g., bar codes, infrared markings, etc.)containing information about vehicle 114. The decal may be locatedoutside vehicle 114, such as on a front or rear bumper, on theunder-side of vehicle 114, or any other location on vehicle 114 wherethe decal may be suitably read. A reader may observe the decal andthereby obtain information about vehicle 114. One implementation employsa bar code placed on the roof of vehicle 114, which can be read by areader placed above vehicle 114.

A receiver may be used to obtain information from an identification tag.According to an implementation of the invention, an antenna may receivesignals transmitted from an identification tag containing a transponder.Any type of conventional receiver may be used to receive signals.According to an implementation of the invention, one reader and/orreceiver may be used in connection with multiple lanes. Based on thesignal received or the decal read, a receiver or reader may determine inwhich lane a particular vehicle is located at a particular time.

According to an implementation of the invention, processor 122 mayreceive vehicle information. For example, processor 122 may receiveinformation about vehicle 114 from a reader and/or receiver. Vehicleinformation and information obtained by sensing vehicle emissions may bestored. Processor 122 may correlate vehicle information received from anidentification tag with the results from vehicle emissions sensing.Processor 122 may update a vehicle record to account for the resultsobtained by processing vehicle emission data, such as informationregarding whether a vehicle has passed or failed predetermined emissionscriteria.

According to an implementation of the invention, RSS 110 may furthercomprise a communication unit 138. Communication unit may communicateinformation such as, for example, measured vehicle emissions andidentification tag information from RSS 110 to various other locations(e.g., Motor Vehicle Departments, a central data repository, servers,etc.) for storage, processing, viewing, or other use in a known manner.Communication unit may transmit and/or receive information via a wiredconnection, such as cable or telephone line, or a wireless connection,such as by a radio, cellular, or satellite transmitter, or via any othertype of suitable wireless communication.

In some implementations, communication unit 138 may comprise appropriatehardware and/or software to enable processor 122 to be accessed remotelyover a network (not illustrated) via a communications link (notillustrated). The network may include any one or more of, for instance,the Internet, an intranet, a PAN (Personal Area Network), a LAN (LocalArea Network), a WAN (Wide Area Network), a SAN (Storage Area Network),or a MAN (Metropolitan Area Network). The communications link mayinclude any one or more of, for instance, a telephone line, a DigitalSubscriber Line (DSL) connection, a Digital Data Service (DDS)connection, an Ethernet connection, an Integrated Services DigitalNetwork (ISDN) line, an analog modem connection, a cable modernconnection, or a wireless connection. In this regard, a user (e.g., anemissions test administrator or other individual) at a remote computerterminal can administer emissions tests, and/or analyze or process data.Thus, RSS 110 may, in various implementations, comprise either manned orunmanned systems.

As recited above, alternative RSS 110 configurations may existincorporating some or all of the aforementioned system components. As anexample, in certain implementations (not illustrated), source 116 anddetector 118 may be placed on opposite sides of roadway 128. Variouscomponents of speed and acceleration detection unit 134 and thermaldetection unit 136 may also be positioned on opposite sides of roadway128.

In another implementation (not illustrated), RSS 110 may comprise acompact, unmanned system that may be used for unattended monitoring ofvehicle emissions data (also referred to as a “bunkered” unit). In suchan implementation, source 116, detector 118, imaging unit 132, processor122, communication unit 138, and various components of speed andacceleration detection unit 134 and thermal detection unit 136 may behoused together on a first side of roadway 128, while transfer optics120 and various other components of speed and acceleration detectionunit 134 and thermal detection unit 136 may be housed together on theopposite side of roadway 128. Other configurations are possible.Accordingly, RSS 110 (as illustrated in FIG. 1) should not be viewed aslimiting.

Detection of Water Droplets in Vehicle Emissions

FIG. 2 is an exemplary illustration of RSS 110, further depictingvarious computer program modules (described in detail below) that may beexecuted on processor 122. Although not all of the components of RSS 110that were depicted in FIG. 1 have been reproduced in FIG. 2, it shouldbe understood that any one or more of the components described withreference to FIG. 1 may be implemented.

As shown in FIG. 2, source 116 may emit electromagnetic radiation atwavelengths that are absorbed by a plurality of molecular speciespresent in vehicle exhaust including, for example, hydrocarbons (HC),carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NO_(X))such as NO and NO₂, and/or other molecular species. As such, thewavelengths at which electromagnetic radiation is emitted by source 116and absorbed by molecular species may include a first absorptionwavelength, a second wavelength, a third absorption wavelength, and/oradditional absorption wavelengths. The first absorption wavelength maybe a wavelength at which a first molecular species absorbselectromagnetic radiation, the second absorption wavelength may be awavelength at which a second molecular species absorbs electromagneticradiation, and the third absorption wavelength may be a wavelength atwhich a third molecular species absorbs electromagnetic radiation.

For instance, the first molecular species may be CO, which may be absorbelectromagnetic radiation at or near 4.6 microns (e.g., the firstabsorption wavelength). The second molecular species may be HC, whichmay absorb electromagnetic radiation at or near 3.6 microns (e.g., thesecond absorption wavelength). The third molecular species may be CO₂,which may absorb electromagnetic radiation at or near 4.3 microns (e.g.,the third absorption wavelength). These are provided merely forillustrative purposes. In some implementations, other particularmolecular species may be used in accordance with this disclosure for thepurposes of detecting the presence of water.

The electromagnetic radiation emitted by source 116 may further includeelectromagnetic radiation at one or more reference wavelengths. The oneor more reference wavelengths may include wavelength(s) at whichelectromagnetic radiation is not substantially absorbed by any of theconstituents commonly found in vehicle exhaust. For example, thereference wavelength may be at or near 3.9 microns.

It will be appreciated that the discussion of individual absorptionand/or reference wavelengths herein may not be restricted to precise,individual wavelengths. As used herein, a given absorption or referencewavelength may include a band of wavelengths around a centralwavelength.

As shown in FIG. 2, processor 122 may be configured to execute one ormore computer program modules. The one or more computer program modulesmay include one or more of a quantity module 210, a ratio module 212, atrigger module 214, a residual module 216, a water analysis module 218,and/or other modules. Processor 122 may be configured to execute modules210, 212, 214, 216, and/or 218 by software, hardware, firmware, somecombination of software, hardware, and/or firmware, and/or othermechanisms for configuring processing capabilities on processor 122.

It should be appreciated that although modules 210, 212, 214, 216, and218 are illustrated in FIG. 2 as being co-located within a singleprocessing unit, in implementations in which processor 122 includesmultiple processing units, one or more of modules 210, 212, 214, 216,and/or 218 may be located remotely from the other modules. Thedescription of the functionality provided by the different modules 210,212, 214, 216, and/or 218 described below is for illustrative purposes,and is not intended to be limiting, as any of modules 210, 212, 214,216, and/or 218 may provide more or less functionality than isdescribed. For example, one or more of modules 210, 212, 214, 216,and/or 218 may be eliminated, and some or all of its functionality maybe provided by other ones of modules 210, 212, 214, 216, and/or 218. Asanother example, processor 122 may be configured to execute one or moreadditional modules that may perform some or all of the functionalityattributed below to one of modules 210, 212, 214, 216, and/or 218.

According to one implementation of the invention, quantity module 210may be configured to obtain preliminary quantities of one or moremolecular species in optical path 130. The quantity module 210 mayobtain the preliminary quantities from one or more external informationresources (not shown) storing previously determined preliminaryquantities of the one or more molecular species. The quantity module 210may obtain the preliminary quantities by determining the quantitiesbased on output signals generated by detector 118 indicating theintensity of electromagnetic radiation received at detector 118 in oneor more absorption wavelengths. The intensities of the electromagneticradiation received in the one or more absorption wavelengths mayindicate an amount of electromagnetic radiation in the one or moreabsorption wavelengths that have been absorbed and/or blocked alongoptical path 130. The quantity module 210 may determine the absorptionof electromagnetic radiation at the one or more absorption wavelengthsbased on the intensity of the electromagnetic radiation emitted bysource 116 at the one or more absorption wavelengths and the outputsignals of detector 118. From the absorption at the one or moreabsorption wavelengths along optical path 130, quantity module 210 maydetermine the preliminary quantities of the corresponding one or moremolecular species. For example, quantity module 210 may determine apreliminary quantity of CO, HC, and/or CO₂.

During operation, the intensities at which electromagnetic radiation atthe one or more absorption wavelengths are emitted by source 116 mayvary. Such variation may be the result of ordinary operation, and/or maybe enhanced by environmental and/or system factors. To account for thesevariations in determining the absorptions of electromagnetic radiationat the one or more absorption wavelengths along optical path 130,detector 118 may generate one or more output signals indicating thereceived intensity of one or more reference wavelengths. Sinceelectromagnetic radiation at the one or more reference wavelengths maynot be significantly absorbed by exhaust gas, quantity module 210 mayimplement these output signals of detector 118 to correct for variationin the intensity of electromagnetic radiation emitted by source 116.

The ratio module 212 may be configured to determine ratios of themolecular species for which quantities are determined by quantity module210. The dilution of exhaust gas present in optical path 130 may not beknown at a given point in time. As such, to determine the concentrationsof molecular species, ratio module 212 determines ratios of molecularspecies because such ratios may be independent of dilution. For example,ratio module 212 may determine a ratio of CO to CO₂, and/or a ratio ofHC to CO₂. The ratios determined by ratio module 212 may be converted toconcentrations of the molecular species from a combustion equation thatassumes a particular fuel.

As previously noted, vehicle exhaust includes relatively largequantities of water. When the water is in a gaseous state, the water maynot substantially interfere with measurements of exhaust gas compositionby RSS 110. However, under certain ambient conditions, such as lowtemperatures and/or high humidity, for example, gaseous water present inexhaust may undergo a phase change and form minute liquid dropletshaving the appearance of white smoke, sometimes incorrectly referred toas “steam” or a “steam plume”. These droplets may effectively blockelectromagnetic radiation at various wavelengths from ultra-violetspectrum, through the visible spectrum, and into the near infra-redspectrum. The wavelengths at which the liquid water blockselectromagnetic radiation may include wavelengths at whichelectromagnetic radiation is absorbed by one or more gaseous species inexhaust gas.

For example, in the spectrum from about 3 microns to about 5 microns,water droplets present in optical path 130 may block electromagneticradiation. This portion of the spectrum may include the first absorptionwavelength, the second absorption wavelength, a third absorptionwavelength, and/or a reference wavelength as described above. In thisportion of the spectrum, the ability of water droplets to blockelectromagnetic radiation may fall as wavelength increases. This drop inblockage of electromagnetic radiation by water droplets may besubstantial for increasing wavelengths. As such, water droplets inoptical path 130 may tend to have a very different impact on theelectromagnetic radiation in optical path 130 at the first absorptionwavelength, the second absorption wavelength, the third absorptionwavelength, and/or the reference wavelength. This may negatively impactthe accuracy of quantity module 210 and/or ratio module 212.

The trigger module 214 may be configured to trigger analysis todetermine if water droplets are present in optical path 130 at a givenpoint in time. This may include analyzing determinations of absorptionand/or quantity of one or more molecular species for apparentlyanomalous readings. By way of non-limiting example, the amount ofblockage caused by water droplets in optical path 130 may be much largerat the second absorption wavelength than in the reference wavelength. Aswas discussed above, quantity module 210 may implement the referencewavelength in determining absorption at the second absorption wavelengthto account for intensity variations at source 116. This may result indeterminations of absorption at the second absorption wavelength (and/orof HC) that are higher than the actual amount of absorption (and/orquantity of HC).

In some implementations, trigger module 214 may monitor determinationsof absorption at the second absorption wavelength and/or determinationsof quantity of HC. The trigger module 214 may trigger analysis todetermine if water is present in optical path 130 if absorption at thesecond absorption wavelength and/or the quantity of HC are elevated. Forexample, further analysis may be triggered by trigger module 214 ifabsorption at the second absorption wavelength and/or the quantity of HCbreach a predetermined threshold.

By way of illustration, FIG. 3 illustrates the manner in which dropletspresent in optical path 130 may cause temporary elevation fordeterminations of absorption of electromagnetic radiation at the secondabsorption wavelength. As can be seen in FIG. 3, the impact of waterdroplets present in optical path 130 on determinations of absorption ofelectromagnetic radiation at the second absorption wavelength, and/ordeterminations of the quantity of HC may be relatively strong. As such,analysis of determinations of absorption of electromagnetic radiation atthe second absorption wavelength that identifies high levels ofelectromagnetic radiation attenuation along optical path 130 may beimplemented to trigger further analysis of the absorption and/orquantity measurements.

Returning to FIG. 2, because of the fall off in blockage by waterdroplets at ascending wavelengths, the blockage by water droplets willtend to impact determinations of absorption for absorption wavelengthsother than the second absorption wavelength differently thandeterminations of absorption for the second absorption wavelength. Thismay enable residual module 216 and water analysis module 218 to detectthe presence of water droplets in optical path 130 from a comparativeanalysis based on the determined absorptions at the various absorptionwavelengths.

The impact of water droplets on the determination of absorption forabsorption wavelengths that are larger than the second wavelength may berelatively small with respect to absorption by exhaust gas along opticalpath 130. As such, before the impact of water droplets on thedeterminations of absorption for absorption wavelengths other than thesecond absorption wavelength can be used to detect the presence of thewater droplets, the impact of the water droplets must be separated fromthe measured absorption by the exhaust gas.

The residual module 216 may be configured to separate the actualabsorption by exhaust gas from residual impact on electromagneticradiation intensity by water droplet blockage at one or more absorptionwavelengths. For example, to quantify the residual impact of waterdroplet blockage at the first absorption wavelength, the quantity of COmay be determined as a function of the quantity of another molecularspecies, such as CO₂. This determination may be made, for instance, by aregression line that correlates values of the quantity of CO determinedby quantity module 210 with values of the quantity of CO₂ determined byquantity module 210 from contemporaneous measurements.

By way of illustration, FIG. 4 illustrates a regression line thatcorrelates determined quantities of CO with determined quantities ofCO₂. FIG. 4 further illustrates residuals from the regression linecorresponding to data points used to determine the regression line. Thisregression line may be associated with a function that describes thequantity of CO as a function of the quantity of CO₂. For example, theequation of the line (e.g., including the slope and intercept) maydescribe the quantity of CO as a function of the quantity of CO₂.

Returning to FIG. 2, once the quantity of CO as a function of CO₂ isdetermined, the residual impact of water droplet blockage at the firstabsorption wavelength (separate from absorption by the first molecularspecies) may be determined according to the following relationship:CO_(residual)=CO_(measured)−(α+m*CO_(2measured))  (2)

where CO_(residual) represents the residual impact of water dropletblockage at the first absorption wavelength on the determination of thequantity of CO;

CO_(measured) represents the quantity of CO determined by the quantitymodule;

CO_(2 measured) represents the quantity of CO₂ determined by thequantity module; and

(α+m*CO_(2measured)) represents a function that describes the quantityof CO as a function of CO_(2measured).

Water droplets formed from exhaust gas will typically only be present inthe optical path for a short period of time. As such, the correlation ofCO_(measured) with CO_(2measured) to determine (α+m*CO_(2measured)),which uses measurements of CO_(measured) and CO_(2measured) over a fargreater period of time than will be impacted by the water droplets, maytend to reflect the relationship between CO_(measured) andCO_(2measured) when water droplets are not present in the optical path.For the purpose of calculation of CO_(residual), if a negativecorrelation slope is obtained (m<0), then the negative in may bereplaced with a 0 in equation (1).

The water analysis module 218 may be configured to analyze the residualimpact of water droplet blockage at the first absorption wavelength onthe determination of the quantity of CO and the quantity of HC made byquantity module 210 to determine if water droplet blockage is/waspresent in optical path 130. For instance, the residual impact of waterdroplet blockage at the first absorption wavelength on the determinationof the quantity of CO may be compared with the quantity of HC todetermine if the values of both of these variables indicate the presenceof water droplet blockage in optical path 130.

By way of non-limiting example, the impact of water droplet blockage ondeterminations of HC may be inversely proportional to the impact ofwater droplet blockage on determinations of CO. In the case of HC andCO, the proportionality factor may be on the order of −10⁻⁴. By way ofillustration, FIG. 5 shows a plot depicting how the quantity of HC maybe correlated with the residual impact of water droplet blockage at thefirst absorption wavelength on the determination of the quantity of COto detect the presence of water droplet blockage. In the plot shown inFIG. 5, water droplets were present in optical path 130. This can beseen from the manner in which the quantity of HC moves inverselyproportionally with the determined residual impact of water dropletblockage at the first absorption wavelength on the determination of thequantity of CO.

If, on the other hand, water droplet blockage were not present, theresidual impact of water droplet blockage at the first absorptionwavelength on the determination of the quantity of CO were notproportional (e.g., inversely proportional) to the determined quantityof HC, water analysis module 218 may determine that water droplets werenot present in optical path 130.

FIG. 6 is an exemplary illustration of a flowchart of processingoperations for detecting the presence of water droplets in the opticalpath of an RSS system, according to an aspect of the invention. Theprocessing operations of method 610 presented below are intended to beillustrative. In some implementations, method 610 may be accomplishedwith one or more additional operations not described, and/or without oneor more of the operations discussed. Additionally, the order in whichthe operations of method 610 are illustrated in FIG. 6 and describedbelow is not intended to be limiting.

In some implementations, method 610 may be implemented in one or moreprocessing devices (e.g., a digital processor, an analog processor, adigital circuit designed to process information, an analog circuitdesigned to process information, a state machine, and/or othermechanisms for electronically processing information). The one or moreprocessing devices may include one or more devices executing some or allof the operations of method 610 in response to instructions storedelectronically on an electronic storage medium. The one or moreprocessing devices may include one or more devices configured throughhardware, firmware, and/or software to execute one or more of theoperations of method 610.

In an operation 612, series of samples related to quantities ofmolecular species present in an exhaust plume may be obtained. Theseries of samples may have been obtained by RSS 110 (as described aboveand illustrated in FIGS. 1 and 2). The series of samples may include,for example, a series of samples related to the quantity of CO, a seriesof samples related to the quantity of HC, and/or a series of samplesrelated to the quantity of CO₂. The series of samples may include aseries of samples of absorption in a first absorption wavelengthassociated with CO, a series of samples of absorption in a secondabsorption wavelength associated with HC, and/or a series of samples ofabsorption in a third wavelength associated with CO₂. The series ofsamples may include a series of samples of measured quantity of CO, aseries of samples of measured quantity of HC, and/or a series of samplesof measured quantity of CO₂.

In an operation 614, a series of samples associated with CO may be maybe analyzed to determine if an analysis for detecting the presence ofwater droplets in the exhaust plume should be performed. Determining ifthe analysis should be performed may include comparing samples relatedto the quantity of HC with a threshold. In some implementations,operation 614 may be performed by a trigger module that is the same asor similar to trigger module 214 (shown in FIG. 2 and described above).If it is determined in operation 614 that the analysis should beperformed, method 610 may proceed to an operation 615.

In operation 615, a relationship between the quantity of CO and CO₂ maybe determined. This relationship may describe the quantity of the firstmolecular species as a function of the quantity of CO₂. Operation 615may include, for example, determining a regression line that plotssamples related to the quantity of CO against contemporaneously measuredsamples of related to the quantity of CO₂. In some implementations,operation 614 may be performed by a residual module that is the same asor similar to residual module 216 (as shown in FIG. 2 and describedabove).

In an operation 616, the quantity of CO may be determined as a functionof the quantity of CO₂. This determination may be made using therelationship determined in operation 615. In some implementations,operation 616 may be performed by a residual module that is the same asor similar to residual module 216 (as shown in FIG. 2 and describedabove).

In an operation 618, the quantity of CO determined according to thefunction determined at operation 616 may be removed from the samplesrelated to the quantity of CO obtained in operation 612. If waterdroplet blockage is present in the samples related to the quantity of COobtained at operation 612, operation 618 may result in the determinationof the residual impact of water droplet blockage on the determination ofthe quantity of CO. In some implementations, operation 618 may beperformed by a residual module that is the same as or similar toresidual module 216 (as shown in FIG. 2 and described above).

In an operation 620, the values obtained in operation 618 are analyzedin conjunction with the samples related to the quantity of HC obtainedin operation 612 to determine whether water droplets were present in theexhaust plume. In some implementations, operation 620 may be performedby a water analysis module that is the same as or similar to wateranalysis module 218 (as shown in FIG. 2 and described above).

If it is determined in operation 620 that water droplets were present inthe exhaust plume one or more of the samples related to the quantity ofHC may be discarded as being inaccurate, may be corrected to adjust forthe impact of the water, and/or may otherwise be processed.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it is to be understood thatthe present invention contemplates that, to the extent possible, one ormore features of any implementation can be combined with one or morefeatures of any other embodiment.

What is claimed is:
 1. A system configured to detect the presence ofwater droplets in vehicle emissions present in an optical path of aremote emissions sensing system, wherein the remote emissions sensingsystem includes an electromagnetic radiation source and a detectorarranged to form the optical path such that the optical path traverses aroadway along which a vehicle travels, the system comprising: one ormore processors configured to execute computer program modules, thecomputer program modules comprising: (i) a quantity module configured toobtain determinations of quantities of a plurality of molecular speciespresent in an exhaust plume emitted by the vehicle, wherein thedetermined quantities of the plurality of molecular species have beendetermined based on output signals generated by the detector conveyinginformation related to intensities of electromagnetic radiation receivedat the detector from the source in a plurality of absorption wavelengthsthat correspond to the plurality of molecular species, wherein theplurality of molecular species comprises carbon monoxide, hydrocarbons,and carbon dioxide, and wherein the plurality of absorption wavelengthscomprises a first absorption wavelength that corresponds to carbonmonoxide, a second absorption wavelength that corresponds tohydrocarbons, and a third absorption wavelength that corresponds tocarbon dioxide; (ii) a residual module configured to determine an impacton determinations of the quantity of carbon monoxide caused by blockageof electromagnetic radiation at the first absorption wavelength by waterdroplets, wherein the residual module is configured to determine animpact on determinations of the quantity of carbon monoxide caused byblockage of electromagnetic radiation at the first absorption wavelengthby water droplets by: determining the quantity of carbon monoxide as afunction of the detected quantity of carbon dioxide; and subtracting thequantity of carbon monoxide determined as a function of detected carbondioxide from the obtained measurement of the quantity of carbonmonoxide; and (iii) a water analysis module configured to detect thepresence of water droplets in the optical path based on a comparativeanalysis of the obtained quantities of hydrocarbons and the determinedimpact on determinations of the quantity of carbon monoxide caused byblockage of electromagnetic radiation at the first absorption wavelengthby water droplets.
 2. The system of claim 1, wherein the residual moduleis further configured to determine a relationship that describes thequantity of carbon monoxide as a function of the measured quantity ofcarbon dioxide.
 3. The system of claim 1, wherein the water analysismodule is configured to detect the presence of water droplets in theoptical path if the determined impact on determinations of the quantityof carbon monoxide caused by blockage of electromagnetic radiation atthe first absorption wavelength is inversely proportional to theobtained quantities of hydrocarbons.
 4. A method of detecting thepresence of water droplets in vehicle emissions present in an opticalpath of a remote emissions sensing system, wherein the remote emissionssensing system includes an electromagnetic radiation source and adetector arranged to form the optical path such that the optical pathtraverses a roadway along which a vehicle travels, the methodcomprising: (i) obtaining measurements of quantities of a plurality ofmolecular species present in an exhaust plume emitted by the vehicle,wherein the measured quantities of the plurality of molecular specieshave been determined based on output signals generated by the detectorconveying information related to intensities of electromagneticradiation received at the detector from the source in a plurality ofabsorption wavelengths that correspond to the plurality of molecularspecies, wherein the plurality of molecular species comprises carbonmonoxide, hydrocarbons, and carbon dioxide, and wherein the plurality ofabsorption wavelengths comprises a first absorption wavelength thatcorresponds to carbon monoxide, a second absorption wavelength thatcorresponds to hydrocarbons, and a third absorption wavelength thatcorresponds to carbon dioxide; (ii) determining, via one or moreprocessors, an impact on determinations of the quantity of the secondmolecular species caused by blockage of electromagnetic radiation at thefirst absorption wavelength by water droplets by: determining thequantity of carbon monoxide as a function of the measured quantity ofcarbon dioxide; and subtracting the quantity of carbon monoxidedetermined as a function of the measured quantity of carbon dioxide fromthe obtained measurement of the quantity of carbon monoxide; and (iii)detecting, via the one or more processors, the presence of waterdroplets in the optical path based on a comparative analysis of themeasured quantities of hydrocarbons and the determined impact ondeterminations of the quantity of carbon monoxide caused by blockage ofelectromagnetic radiation at the first absorption wavelength by waterdroplets.
 5. The method of claim 4, wherein determining an impact ondeterminations of the quantity of carbon monoxide caused by blockage ofelectromagnetic radiation at the first absorption wavelength by waterdroplets further comprises determining a relationship that describes thequantity of carbon monoxide as a function of the measured quantity ofcarbon dioxide.
 6. The method of claim 5, wherein determining therelationship that describes the quantity of carbon monoxide as afunction of the measured quantity of carbon dioxide comprisesdetermining a regression line that correlates the obtained measurementsof carbon monoxide with the obtained measurements of carbon dioxide. 7.The method of claim 4, wherein the presence of water droplets in theoptical path is detected responsive to the determined impact ondeterminations of the quantity of carbon monoxide caused by blockage ofelectromagnetic radiation at the first absorption wavelength beinginversely proportional to the obtained quantities of the first molecularspecies.
 8. A system configured to detect the presence of water dropletsin vehicle emissions present in an optical path of a remote emissionssensing system, wherein the remote emissions sensing system includes anelectromagnetic radiation source and a detector arranged to form theoptical path such that the optical path traverses a roadway along whicha vehicle travels, the system comprising: one or more processorsconfigured to execute computer program modules, the computer programmodules comprising: (i) a quantity module configured to obtaindeterminations of quantities of a plurality of molecular species presentin an exhaust plume emitted by the vehicle, wherein the determinedquantities of the plurality of molecular species have been determinedbased on output signals generated by the detector conveying informationrelated to intensities of electromagnetic radiation received at thedetector from the source in a plurality of absorption wavelengths thatcorrespond to the plurality of molecular species, wherein the pluralityof molecular species comprises a first molecular species and a secondmolecular species, and wherein the plurality of absorption wavelengthscomprises a first absorption wavelength that corresponds to the firstmolecular species and a second absorption wavelength that corresponds tothe second molecular species; (ii) a residual module configured todetermine an impact on determinations of the quantity of the firstmolecular species caused by blockage of electromagnetic radiation at thefirst absorption wavelength by water droplets; and (iii) a wateranalysis module configured to detect the presence of water droplets inthe optical path based on a comparative analysis of the obtainedquantities of the second molecular species and the determined impact ondeterminations of the quantity of the first molecular species caused byblockage of electromagnetic radiation at the first absorption wavelengthby water droplets.
 9. The system of claim 8, wherein the first molecularspecies is carbon monoxide and the second molecular species ishydrocarbon.
 10. The system of claim 8, wherein the plurality ofmolecular species further comprises a third molecular species, whereinthe plurality of absorption wavelengths comprises a third absorptionwavelength that corresponds to the third molecular species, and whereinthe residual module is configured to determine an impact ondeterminations of the quantity of the first molecular species caused byblockage of electromagnetic radiation at the first absorption wavelengthby water droplets by: determining the quantity of the first molecularspecies as a function of the measured quantity of the third molecularspecies; and subtracting the quantity of the first molecular speciesdetermined as a function of the measured quantity of the third molecularspecies from the obtained measurement of the quantity of the firstmolecular species.
 11. The system of claim 10, wherein the thirdmolecular species is carbon dioxide.